Ashlee Simpson and Evan Ross celebrated two things last night: Their engagement and Simpson's future mother-in-law Diana Ross' birthday! The couple, who got engaged in January, threw an engagement party on Wednesday, which happened to be the same day the groom-to-be's mother turned 70 years old. Ashlee tweeted about the bash and even shared a sweet photo from the event, which showed her and her fiancé embracing each other and wearing festive crowns and fur.

Ashlee's big sister Jessica got in on the social media action, too, posting the below photo with the caption: "Celebrating my best friend and sister @missbananahammock @ashleesimpsonofficial. I love her so much!" (Jessica knows a thing or two about weddings at this point; the singer-turned-businesswoman has been engaged to fiancé Eric Johnson since November 2010 and is reportedly planning to get married this spring.)

Considering it was the mother-of-the-groom's birthday, we wonder if the living legend gave a special private performance in honor of her son and his fiancée? If she decided to rest her vocal cords instead, we do know that she is actively involved in helping the couple plan their wedding. "She's involved in all levels of my life. She's one of the most incredible mothers ever," Ross, who was in The Hunger Games: Catching Fire, told E! News a few weeks ago at SXSW in Austin, Texas. "She's involved in every piece of our wedding [and] engagement party."

Though they haven't announced a wedding date, Simpson and Ross seem ready to tie the knot in a moment's notice. "Honestly, we could go and get married right now, wherever," Ross added. "We just want to be married. We're in love. This is the most incredible time I could ever think of in my life and I'm young, but the same time, I've lived a different life than most and I can't think of a happier moment."